Superconducting Double Transition and the Upper Critical Field Limit of Sr2RuO4 in Parallel Magnetic Fields

TL;DR

This study reveals a double transition in Sr2RuO4's superconducting phases and identifies a limit to the upper critical field Hc2 for in-plane magnetic fields, indicating complex phase behavior.

Contribution

First thermodynamic evidence of multiple superconducting phases in Sr2RuO4 and identification of Hc2 limiting behavior for parallel magnetic fields.

Findings

Double peak structure in superconducting transition under magnetic field.

Limiting of Hc2 occurs within 2 degrees of the field orientation.

Hc2 limiting and multiple phases likely share a common physical origin.

Abstract

We studied the specific heat and thermal conductivity of the spin-triplet superconductor Sr2RuO4 at low temperatures and under oriented magnetic fields H. We resolved a double peak structure of the superconducting transition under magnetic field for the first time, which provides thermodynamic evidence for the existence of multiple superconducting phases. We also found a clear limiting of the upper critical field Hc2 for the field direction parallel to the RuO2 plane only within 2 degrees. The limiting of Hc2 occurs in the same H-T domain of the second superconducting phase; we suggest that the two phenomena have the same physical origin.